Non-magnetic or feebly magnetic diamond sintered compact and a process for the productin of the same

ABSTRACT

The object of the present invention is to provide a non-magnetic or feebly magnetic diamond sintered compact available for a magnetic article or magnetic material. This object can be achieved by a non-magnetic or feebly magnetic diamond sintered compact whose magnetic susceptibility is at most 3% of Fe, consisting of a high hardness sintered compact comprising at least 50 volume % of diamond with a grain size of 0.1 to 100 μm and a binder phase containing a metallic component selected from the group consisting of ferromagnetic iron group metals such as Ni, Co, Fe, etc. and mixtures thereof, in which at least one of feebly magnetic metal components each having a magnetic susceptibility of at most 5×10 -8  (emu/g), for example, Cr, V, Cu, Si, Zn, Al Mo, W, etc. is dissolved in a proportion of 1 to 50 volume % to the binder phase to form an alloy, whereby the magnetic moment of the diamond sintered compact having the binder phase containing the iron group metals and others, as a predominant component, is decreased by at least 80%.

TECHNICAL FIELD

This invention relates to a diamond sintered compact additionallyprovided with properties suitable for, in particular, an edge of acutting tool and a wear resistance tool and more particularly, it isconcerned with a nonmagnetic or feebly magnetic diamond sintered compactwhose magnetic susceptibility is at most 3% of Fe.

In particular, the diamond sintered compact of the present invention canbe applied to a wear resistance tool during transporting a magneticproduct or producing a magnetic material utilizing the feature of thefeeble magnetism thereof.

BACKGROUNDS TECHNIQUES

A diamond sintered compact, obtained by sintering fine diamond grainswith an iron group metal such as Co, as a binder, at an ultra-highpressure and high temperature under which diamond is thermodynamicallystable, has widely been used for cutting tools, wear resistance tools,wire-drawing dies, etc. utilizing its excellent strength as well as wearresistance. However, it is difficult at the present time to use, as awear resistance tool for magnetic products, commercially availablediamond compacts, the most part of which are produced by infiltrating Coin a diamond powder from WC--Co cemented carbides at an ultra-highpressure and high temperature, as described in Japanese PatentPublication No. 12126/1977 to give a ferromagnetic material.

A method comprising dissolving a feebly magnetic metal component in aferromagnetic iron group metal and thereby changing the magnetic momenthas been known, as exemplified by a graph showing a change of magneticmoment of Ni shown in FIG. 1 and FIG. 2 from "Handbook of Magnetism(Jisei Binran)". Japanese Patent Publication No. 14107/1986 describes adiamond sintered compact in which iron group metals and carbides,nitrides and borides of Ti, Zr, Hf, V, Nb, Ta and Cr are dissolved in abinder phase of diamond, but this aims at preventing grain growth ofdiamond and is silent as to the magnetic property.

As the magnetism-free diamond sintered compact, there are marketed adiamond sintered compact from which the binder metal is leached with anacid, as disclosed in U.S. Pat. No. 4224380 and a diamond sinteredcompact using a ceramic material such as SiC, etc. as a binder, asdisclosed in Japanese Laid-Open Publication No. 236650/1986. Thesediamond sintered compacts do not have magnetism, nor simultaneouslyallow electric current to pass, so an electric discharge working,commonly used as a working method of diamond, cannot be used but thecompacts are applied to only limited uses such as fine wire drawing diesfor laser working.

When using the diamond sintered compacts of the prior art as a wearresistance tool of a claw or absorption nozzle for transporting orconveying magnetic products, the products tend to adhere to the tool andis hardly peeled off, or the positioning precision during transportingis deteriorated to result in difficulty in use of the tool. As a wearresistance tool during producing a magnetic material such as a guide fora magnetic tape, they cannot be used because of checking the magneticproperty of the products.

The principal object of the present invention is to provide anon-magnetic or feebly magnetic diamond sintered compact capable ofsolving these problems and being applied to magnetic products ormagnetic materials.

DISCLOSURE OF THE INVENTION

The inventors have made various efforts to overcome the disadvantagethat the diamond sintered compacts of the prior art have strongmagnetism and consequently, have succeeded in decreasing the magneticmoment of an iron group metal in the binder phase by at least 80% whilemaintaining the bonding strength of diamond grains with each other as itis by dissolving a predetermined amount of another feebly magnetic metalcomponent in the binder phase of the iron group metal, and thereby alsodecreasing the magnetic moment of the diamond sintered compact itself byat least 80%.

That is to say, the present invention provides a non-magnetic or feeblymagnetic diamond sintered compact whose magnetic susceptibility is atmost 3% of Fe, consisting of a high hardness sintered compact comprisingat least 50 volume % of diamond with a grain size of 0.1 to 100 μm and abinder phase containing a metallic component selected from the groupconsisting of ferromagnetic iron group metals such as Ni, Co, Fe, etc.and mixtures thereof, in which at least one of feebly magnetic metalcomponents each having a magnetic susceptibility of at most 5×10⁻⁶(emu/g), for example, Cr, V, Cu, Si, Zn, Al, Mo, W, etc. is dissolved ina proportion of 1 to 50 volume % to the binder phase to form an alloy,whereby the magnetic moment of the diamond sintered compact having thebinder phase containing the iron group metals and others, as apredominant component, is decreased by at least 80%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a change of magnetic moment of Ni by forming asolid solution with a feebly magnetic metal.

FIG. 2 is another graph showing a change of magnetic moment of Ni byforming a solid solution with a feebly magnetic metal.

FIG. 3 is a schematic view of a capsule structure for the production ofa diamond sintered compact shown in Example 1.

FIG. 4 is an electron micrograph showing a bonded alloy structure of thediamond sintered compact obtained by the method shown in Example 1.

BEST EMBODIMENT FOR CARRYING OUT THE INVENTION

In the present invention, it is effective to use, as a metalliccomponent to be dissolved in the iron group metal, feebly magneticmetals each having a magnetic susceptibility of at most 5×10⁻⁶ (emu/g)such as Cr, V, Cu, Mo, Al, W, Si, Zn, etc. Cf. Magnetic Susceptibilityof Elements shown in "Handbook of Magnetism (Jisei Binran)"!, but theeffect of decreasing magnetism cannot effectively be exhibited unlessthe microscopic dispersibility of the binder phase metal is uniform forthe same binder phase metallic component. In order to solve thisproblem, the following two methods are taken into consideration, i.e. 1a method comprising rendering metallic component grains finer thandiamond grains to be the binder phase and said diamond grains as thepredominant component and previously dispersing them uniformly and 2method comprising uniformly infiltrating a metallic component to be thebinder phase into diamond grains under the diamond sintering conditionsat an ultra-high pressure and a high temperature. However, it is foundmost effective to infiltrate, by the method 2, the metallic componenthaving the binder phase composition into the raw material powders,previously mixed with 1 to 90% of the metallic component in the binderphase by the method 1. Production of the raw material powders of 1 isgenerally carried out by a method comprising using a metallic powderhaving a finer grain size than the raw material diamond powder, or amethod comprising mixing with a metal oxide or metal carbide having a 1to 3 times coarser grain size than the raw material diamond powder andthen subjecting the mixture to mechanical crushing to render it finerthan the diamond powder, followed by a reducing treatment, etc.

For the production of the non-magnetic or feebly magnetic diamondsintered compact according to the present invention, the commonly usedcemented carbides such as WC-10% Co, We-8% Co, etc., cermets such asMoC-15% Ni-5% Co, etc. can also be used as a high strength metal carbideto be bonded with the sintered compact. As a non-magnetic or feeblymagnetic metal carbide to be bonded with the sintered compact, there canbe used non-magnetic cemented carbides with a composition of WC--Ni--Cr,for example, WC-12% Ni-0.6% Cr, WC-8% Ni-0.4% Cr, etc. These materialscan be used in the form of either a previously sintered compact or insitu sintered compact.

The present invention has succeeded in reduction of the magnetism of adiamond sintered compact, as illustrated above, but the diamond sinteredcompact has generally been commercially available as a jointed articlefor the purpose of improving the brazing strength or reinforcing and thecemented carbide used as a jointed article with the diamond sinteredcompact generally comprises a high hardness metal carbide such as WC,etc. sintered with an iron group metal such as Co or Ni as a binder tobe ferromagnetic. Even if a non-magnetic or feeble magnetic diamondsintered compact is prepared, therefore, combination thereof with theordinary cemented carbides to form a jointed article results in aferromagnetic body as a whole. The present invention has succeeded inrendering non-magnetic or feebly magnetic a diamond sintered compact, asa whole, even in the form of a jointed article with the ordinarily andcommercially available cemented carbides by the use of a non-magnetic orfeebly magnetic cemented carbide for the jointed article, the cementedcarbide containing a binder in which a feebly magnetic metal isdissolved.

A procedure for obtaining a non-magnetic or feebly magnetic alloy bydissolving a feebly magnetic metallic component in a ferromagnetic irongroup metal has been known and has widely been applied to stainlesssteels, etc. In the present invention, this technique is applied toreduction of the magnetism of a binder metallic component duringproducing a diamond sintered compact. The reason why such a techniquehas not been applied to a diamond sintered compact up to the presenttime lies in difficulty of uniformly dispersing many kinds of metalliccomponents in the diamond sintered compact. In order to solve thisproblem, it has been employed to use an ultra-fine metallic powderhaving a smaller grain size than diamond powder or to use a powder ofmetal carbide or oxide having such a hardness as can readily be crushedin a step of crushing and crush the powder while mixing with the diamondpowder as the raw material. Thus, many kinds of the metallic componentswith a finer grain size than the raw material diamond powder canuniformly be dispersed and a non-magnetic or feebly magnetic diamondsintered compact is developed. Furthermore, it is found that a blankmaterial of a non-magnetic or feebly magnetic diamond sintered compacthaving the same shape, in general, as commercially available blankmaterials of diamond sintered compacts can be provided by bonding thenon-magnetic or feebly magnetic diamond sintered compact with anon-magnetic or feebly magnetic cemented carbide.

The embodiments of the present invention are summarized below:

(1) A non-magnetic or feebly magnetic diamond sintered compact providedwith a high strength metal carbide alloy, wherein the non-magnetic orfeebly magnetic diamond sintered compact described in embodiments 1 or 2is produced in contact with a high strength metal carbide alloy.

(2) The non-magnetic or feebly magnetic diamond sintered compactprovided with a high strength metal carbide alloy, described in theabove (1), wherein the high strength metal carbide alloy is WC sinteredwith 3 to 20 weight % of Co.

(3) A non-magnetic or feebly magnetic diamond sintered compact providedwith a non-magnetic or feebly magnetic metal carbide alloy, whosemagnetic susceptibility, as a whole, is at most 3% of Fe, wherein thenon-magnetic or feebly magnetic diamond sintered compact described inembodiments 1 or 2 is produced in contact with a non-magnetic or feeblymagnetic metal carbide alloy.

(4) The non-magnetic or feebly magnetic diamond sintered compactprovided with a non-magnetic or feebly magnetic metal carbide alloy,described in the above (3), wherein the non-magnetic or feebly magneticmetal carbide alloy is WC sintered with 5 to 25 weight % of Ni and 5 to25 weight %, based on Ni, of Cr.

(5) A process for the production of a non-magnetic or feebly magneticdiamond sintered compact, described in embodiments 1 to 4, whichcomprises sintering a raw material powder obtained by mixing diamondpowder, as a predominant component, with a metal to be a binder phaseand a metallic component to be dissolved in the binder phase, crushed togive a grain size of smaller than the diamond powder as a predominantcomponent, under conditions of the diamond-stable range.

(6) A process for the production of a raw material powder of anon-magnetic or feebly magnetic diamond sintered compact, described inembodiments 5, wherein the metallic component is a metal oxide or ametal carbide having such a hardness as can be crushed in a crushingstep by an attriter, ball mill, shaker mixer, etc. to give a grain sizeof smaller than the diamond powder, and after mixing these materials,the metallic component having a grain size of smaller than the diamondpowder is precipitated, for example, by a reducing treatment.

(7) A process for the production of a non-magnetic or feebly magneticdiamond sintered compact, described in embodiments 1 to 4, whichcomprises infiltrating 10 to 99% of a metal to be the binder phase and ametallic component to be dissolved in the binder phase into a rawmaterial powder, obtained by mixing a diamond powder with a metal to bethe binder phase and a metallic component to be dissolved in the binderphase by the method described in embodiment 5 or 6, from the metal andmetal carbide alloy in contact with the raw material powder andsimultaneously sintering, under sintering conditions in thediamond-thermodynamically-stable range at an ultra-high pressure andtemperature.

The present invention will specifically be illustrated by the followingExamples.

(Example 1)

10 weight %, based on the weight of diamond powder, of a Ni oxide powderhaving a grain diameter of 1 μm and 5 weight % of a Cr carbide powderhaving a grain diameter of 5 μm were added to the diamond powder havinga grain diameter of 1/2 to 2 μm, crushed and mixed in a ball mill andthen subjected to a reducing treatment at 1100° C. in a vacuum furnaceto prepare a raw material powder. This raw material powder 2 was chargedin a container 1 made of a non-magnetic cemented carbide with acomposition of WC-8 weight % Ni-0.4 weight % Cr, in which Ni metal 3 andMo metal 4 for infiltration were further inserted on one side thereof,and then covered with a cemented carbide plate 5 to form a capsule (Cf.FIG. 3). The resulting capsule was compressed to 5 GPa using anultra-high pressure and high temperature apparatus used for thesynthesis of diamond, then subjected to temperature rising to 1400° C.and maintained for 20 minutes. After lowering the temperature andpressure, the cover of the cemented carbide was cut and removed toobtain a diamond sintered compact fitted with a non-magnetic cementedcarbide. When the magnetism of the diamond sintered compact was measuredby a ferrite content meter, the magnetic susceptibility is only 0.3% ofFe, corresponding to 6% of the magnetic moment of a diamond sinteredcompact prepared, for comparison, adding no Cr carbide to the rawmaterial and using no Mo plate for infiltration in the above describedprocedure. Namely, it was favorably carried out to lower the magneticmoment by at least 90%. When the diamond sintered compact of the presentinvention was subjected to a lapping working and examination of thebonded state of diamond, it was confirmed to be a uniform sinteredcompact, as shown in a metallic microphotograph of FIG. 4(magnification: ×1000). According to this preparation procedure,moreover, there was obtained a feebly magnetic diamond sintered compactblank material provided with a non-magnetic cemented carbide, whosewhole magnetic susceptibility was at most 0.3% of Fe.

(Example 2)

When a diamond sintered compact was prepared from the raw materialpowder of Example 1 in the same procedure of Example 1 except using noMo plate for infiltration and subjected to estimation in the same manneras Example 1, the magnetism of the diamond sintered compact was loweredby only 50%. It was confirmed that the synergistic effect of decreasingthe magnetic moment was generated by using two or more feebly magneticmetal components to be dissolved.

(Example 3)

When a diamond sintered compact was prepared in an analogous manner toExample 1 except charging the raw material of Example 1 in a cementedcarbide of WC-8 weight % Co and subjected to estimation in an analogousmanner to Example 1, the magnetic moment of the diamond sintered compactwas lowered by 90%. According to this preparation procedure, there wasobtained a feebly magnetic diamond sintered compact blank materialprovided with a ferromagnetic cemented carbide.

(Example 4)

10 weight %, based on the weight of diamond powder, of metallic Nipowder having a grain diameter of 1 μm, 5 weight % of a Cr carbidepowder having a grain diameter of 5 μm and 2 weight % of a Cu oxidepowder having a grain diameter of 2 μm were added to the diamond powderhaving a grain diameter of 2 to 4 μm, crushed and mixed in a ball milland then subjected to a reducing treatment at 1100° C. in a vacuumfurnace to prepare a raw material powder. This raw material powder wascharged in a container made of a non-magnetic cemented carbide with acomposition of WC-8 weight % Ni-0.4 weight % Cr, in which Ni metal andAl metal for infiltration were further inserted on one side thereof, andthen covered with a cemented carbide plate to form a capsule. Theresulting capsule was compressed to 5 GPa using an ultra-high pressureand high temperature apparatus used for the synthesis of diamond, thensubjected to temperature rising to 1400° C. and maintained for 20minutes. After lowering the temperature and pressure, the cover of thecemented carbide was cut and removed to obtain a diamond sinteredcompact fitted with a non-magnetic cemented carbide. When the magnetismof the diamond sintered compact was measured by a ferrite content meter,the magnetic susceptibility is only 1.0% of Fe, corresponding to 18% ofthe magnetic moment of a diamond sintered compact prepared, forcomparison, adding no Cr carbide, nor Cu oxide to the raw material andusing no Mo plate for infiltration in the above described procedure.Namely, it was favorably carried to lower the magnetic moment by atleast 80%.

Utility and Possibility on Commercial Scale

As illustrated above, the non-magnetic or feebly magnetic diamondsintered compact obtained by the present invention can effectively beapplied to a wear resistance tool for transporting a magnetic productcausing a problem on magnetism or a wear resisting part such as a guide,etc. during producing a magnetic material. In particular, thenon-magnetic or feebly magnetic a diamond sintered compact fitted with anon-magnetic or feebly magnetic metal carbide alloy, prepared in theform of a jointed article with the non-magnetic or feebly magneticcemented carbides, can readily be worked in the same shape as that ofthe commercially available diamond sintered compact blank materialfitted with any shape of the cemented carbide and can thus be used inall fields of wear resistance articles causing problems on magnetism,thereby markedly improving the service life of the prior art articlesutilizing the high hardness property of diamond.

We claim:
 1. A non-magnetic or feebly magnetic diamond sintered compactwhose magnetic susceptibility is at most 3% of Fe, consisting of a highhardness sintered compact comprising at least 50 volume % of diamondpowder with a grain size of 0.1 to 100 μm and a binder phase containingat least one metallic component selected from the group consisting offerromagnetic iron group metals and mixtures thereof, in which at leastone of feebly magnetic metal components each having a magneticsusceptibility of at most 5×10⁻⁶ (emu/g) is dissolved in a proportion of1 to 50 volume % to the binder phase to form an alloy, whereby themagnetic moment of the diamond sintered compact having the binder phasecontaining the group of iron group metals, as a predominant component,is decreased by at least 80%.
 2. The non-magnetic or feebly magneticdiamond sintered compact as claimed in claim 1, wherein theferromagnetic iron group metals are Ni, Co and Fe and the feeblymagnetic metal components are Cr, V, Cu, Si, Zn, Al, Mo and W.
 3. Anon-magnetic or feebly magnetic diamond sintered compact provided with ahigh strength metal carbide alloy, wherein the non-magnetic or feeblymagnetic diamond sintered compact described in claim 1 is produced incontact with a high strength metal carbide alloy.
 4. A non-magnetic orfeebly magnetic diamond sintered compact provided with a non-magnetic orfeebly magnetic metal carbide alloy, whose magnetic susceptibility, as awhole, is at most 3% of Fe, wherein the non-magnetic or feebly magneticdiamond sintered compact described in claim 1 is produced in contactwith a non-magnetic or feebly magnetic metal carbide alloy.
 5. A processfor the production of a nonmagnetic or feebly magnetic diamond sinteredcompact, described in any one of claims 1 to 4, which comprisessintering a raw material powder obtained by mixing diamond powder, as apredominant component, with a metal to be a binder phase and a metalliccomponent to be dissolved in the binder phase, crushed to give a grainsize of smaller than the diamond powder as a predominant component, saidsintering being performed under conditions in the diamond-stable range.6. A process for the production of a raw material powder for anon-magnetic or feebly magnetic diamond sintered compact, described inclaim 5, wherein the metallic component is a metal oxide or a metalcarbide having such a hardness as can be crushed in a crushing step byan attriter, ball mill or shaker mixer, to give a grain size of smallerthan the diamond powder, and after mixing these materials, the metalliccomponent having a grain size of smaller than the diamond powder isproduced by a reducing treatment.
 7. A process for the production of anonmagnetic or feebly magnetic diamond sintered compact, described inany one of claims 1 to 4, which comprises infiltrating 10 to 99% of ametal to be the binder phase and a metallic component to be dissolved inthe binder phase into a raw material powder, wherein the raw materialpowder is prepared by a) mixing diamond powder with a metal to be abinder and a metallic component to be dissolved in the binder phase andcrushing the mixture to give a grain size of smaller than the diamondpowder or b) mixing diamond powder with a metal to be a binder and ametal oxide or metal carbide having such a hardness as can be crushed ina crushing step to give a grain size of smaller than the diamond powder,to be dissolved in the binder phase, crushing the mixture and reducingthe metal oxide or metal carbide, and simultaneously sintering the metaland metal carbide alloy in contact with the raw material powder, undersintering conditions in the diamond-thermodynamically-stable range at anultra-high pressure and temperature.